Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 150131
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
930 PM EDT TUE OCT 14 2014

...VALID 03Z WED OCT 15 2014 - 00Z THU OCT 16 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W 45J 25 SE UZA 25 NE GRD 10 NNW GRD 15 SE AND 15 SW CEU
20 W CEU 15 SSE 1A5 20 N 1A5 40 ENE TYS 30 ESE 1A6 40 WNW I16
CRW 20 S W22 25 NW W99 20 SSW CBE 25 WNW OKV 10 S OKV CHO
15 SSW FVX 15 NNE TDF IGX 15 N SOP 10 N 45J 20 W 45J.



...MID ATLANTIC...

A 40 TO 45 KNOT LOW LEVEL JET (AS SHOWN BY REGIONAL VWP ACROSS THE
SOUTHEAST) CONTINUES TO TRANSPORT PRECIPITABLE WATER VALUES
BETWEEN 1.60 AND 2.00 INCHES (WHICH IS ABOUT TWO STANDARD
DEVIATIONS ABOVE NORMAL). THE BEST INSTABILITY REMAINS ANCHORED
OVER THE SOUTHEAST AND COASTAL MID ATLANTIC. SHOWERS AND EMBEDDED
LOW TOPPED CONVECTION STREAMS NORTH THROUGH THE INTERIOR MID
ATLANTIC
AND EASTERN OH VALLEY. AS THE BEST INSTABILITY SHRINKS BACK TOWARD
THE SOUTHEAST COAST THIS EVENING...AND THE AMOUNT OF EMBEDDED
CONVECTION ACROSS THE OH VALLEY AND MID ATLANTIC SHOULD WANE. THE
EXCEPTION COULD BE ACROSS NORTHWEST SC INTO WESTERN NC AND
WESTERNMOST VA. CONVECTION MOVING NORTH IN A POOL OF HIGH
PRECIPITABLE WATER AIR AND ENOUGH INSTABILITY FOR CONVECTION MAY
DROP AS MUCH AS 1.50 INCHES OF RAINFALL IN AN HOUR. THE LATEST
HRRR AND RAP SUGGEST THAT THE INSTABILITY WANES AS THE
PRECIPITABLE WATER AXIS MOVES SLOWLY EAST. AT THIS POINT...A
THREAT REMAINS AS ONE AND THREE HOUR FLASH FLOOD GUIDANCE VALUES
HAVE BEEN LOWERED DUE TO EARLIER HEAVY RAIN. THE THREAT SHOULD
CONTINUE THROUGH ABOUT 05Z.

THE HIGH MOISTURE CONTENT AIR SHOULD CONTINUE TO FEED AREAS OF
SHOWERS AND LOW TOPPED CONVECTION THROUGH AT LEAST 15/12Z. THE
PREPONDERANCE OF HIGH RESOLUTION GUIDANCE SUGGESTS THAT ANOTHER
LINE OF MOSTLY LINEAR CONVECTION WILL AFFECT WV THROUGH CENTRAL NC
INTO SC DURING THE OVERNIGHT HOURS. THERE ARE SOME TIMING AND
PLACEMENT ISSUES WITH THE LINE OR LINES OF CONVECTION...AND THIS
IMPACTS THE AMOUNT OF QPF. FOR THE MOST PART...THE THREAT FOR
HEAVY TO EXCESSIVE RAINFALL IS BEST BETWEEN 15/06Z AND 15/12Z IN
THE ABOVEMENTIONED AREAS. MUCH OF THE GUIDANCE SHOWS BETWEEN 1 AND
2 INCHES OF QPF WITH THE LINEAR CONVECTION...WHICH SEEMS
REASONABLE SINCE THE CONVECTION SHOULD BE MOVING...AT LEAST
INITIALLY. BOTH THE LATEST HRRR AND ARW SHOW BETWEEN 2 AND 4
INCHES OF QPF WITH THE LINE... MAINLY FROM EASTERN WV INTO
NORTHERN SC. IT IS DIFFICULT TO DETERMINE SHOW MUCH INSTABILITY
WILL BE AVAILABLE FOR CONVECTION...SINCE THE 15Z SREF MEAN SHOWS
CAPE VALUES DROPPING BELOW 500 J/KG IN THE ABOVEMENTIONED AREAS
AFTER ABOUT 15/03Z. HOWEVER...1.00 TO 2.00 INCHES OF BASIN
AVERAGED QPF IS EXPECTED ACROSS INTERIOR SECTIONS OF THE MID
ATLANTIC THROUGH ABOUT 12Z. BECAUSE OF THE SIGNAL IN THE LATEST
HIGH RESOLUTION GUIDANCE...THE SLIGHT RISK AREA WAS EXPANDED
EASTERN INTO CENTRAL NC AND CENTRAL VA.

AFTER 15/12Z...PRECIPITABLE WATER VALUE START DROPPING AS THE LOW
LEVEL JET STARTS TO WEAKEN A BIT. BY THAT TIME...WITH MARGINAL
INSTABILITY...MUCH OF THE QPF WOULD OCCUR MAINLY WITH BATCHES OF
SHOWERS AND EMBEDDED CONVECTION...SUGGESTING MORE OF A FLOOD
RATHER THAN FLASH FLOOD THREAT.

HAYES
$$





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